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Discussion Starter #1
So while I was at the junkyard hunting for a manual steering gearbox, I decided to grab a pedal assembly to use as a throttle. I want to say it was out of a 2002 Subaru Impreza (that had seem better days). I sliced off as much of the wiring as I could get at, and figured it would be no problem to look up the pin-outs and figure out what everything did... For the life of me I can not seem to find any info on it. There are 6 wires, and I have done enough reading to know that there should be 2 hall-effect sensors in there: so 2x +5v 2x ground and 2x signals.

What I want to ask is, how sensitive are these things? Can I just go ahead and apply 5 volts and ground willy nilly, and see if I get a signal on one of the other wires when I push on the pedal? Would there be electrical continuity/a specified resistance between 5v and ground? Would appreciate any input if one of you all have been down this road before. If I really screw it up, I guess I can always go get another one. They only cost like 7.50 at the pick-n-pull.
 

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Are you sure about the year and what type of accelerator pedal position sensor is being used? a picture might help to rule out the sliding wiper type versus the hall sensor type. It appears they have used several varieties over the years with no consistancy in the wiring pinouts.

If you can get the service manual and find the troubleshooting section for P2138 it might give details for the wiring and connector.
 

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Discussion Starter #3
Hey Kennybobby, thanks for that picture! I sliced off the wires that came out of the harness, and that top layout seems to be nearly an exact match. One of the red wires on my pedal looks like it has a green stripe, but your diagram says it should be blue like the other one. At any rate, that should hopefully give me a good place to start my testing.

I will post a picture and an update when I get back up to the shop next.
 

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that diagram can't be correct--you wouldn't have both +5 and ground using the same wire color, so it is probably a typo in the diagram.

Hall sensors are ESD sensitive and can be easily blown by reverse and too high voltages, so be careful before hitting it with full power. Use a current-limited power supply, but use a meter to ring it out first.
 

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Discussion Starter #5
Thanks, Kennybobby, sounds like it might be wise to go down the rabbit hole, and actually understand how this thing actually works. Perhaps this information will be useful to anyone else who wants to decipher a different HEPA unit. I found a diagram of a hall-effect sensor, and I think I understand the basic principle, but I am not quite clear on the specifics.


Now this is just the sensor itself; am I right that the Hall voltage is going to be tiny, and that there is some sort of amplifier circuit that is raising the output up to what we would expect to see from the pedal (0.6-3.6 volts or whatever it is)?

So if I understand correctly, 5 volts is fed into the semiconductor, and there is then a circuit that also runs off that 5 volts and returns a signal that correlates to the hall voltage. I am guessing it is this amplifier circuit that is going to be sensitive to abuse?

My plan had been to strip the wires from a USB charger to get my 5 volts (looks like the smallest one I have is 700mA - which seems like a lot) I am not sure what you mean by "use a meter to ring it out" - could you outline what you do to try and verify the pins if you assumed your only tools were a dismantled phone charger and a cheap multimeter? (Even if your answer involves buying a better power supply, I still would like to hear it, as I feel like the information might be of use to others) Anyway, thanks for the input, and, as always, would love to hear from anyone who has "been there and done that"!
 

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Discussion Starter #6
Okay, snapped a few piuctures of the pedal that I found. Now that I think about it, 2002 does not sound right, it probably was an '07.





I am going to plan on wiring it up per the diagram shown above, and see if I get a variable signal out. Does anyone have a suggestion for how to go about verifying that I am wiring it correctly before applying voltage? Has anyone used one of these pedal assemblies for their build? EV West wanted like 80 bucks for something similar, so repurposing stuff from the pick-n-pull seems like a good way to go.
 

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i found a wiring diagram online for the 2005 and it shows a resistance wiper type of pedal position sensor. Haven't been able to find the 2007 to verify the type or the wire color. Kinda crappy manual to not have wire colors, almost useless in fact.

but the numbering/positions seems to agree with the 2005 version with the wire colors, hopefully the 2007 is somewhat correct also.

Also found a picture of the 2009 pedal, it looks like yours but i couldn't find the wiring. But now i can't add pictures ?

But what a mess is a subaru--every damn one has a different color scheme for the APPS. i looked thru and found many but couldn't find the colors of yours. So when you figure this out you need to post your findings to help out the next guy.

Link to FSM with wire colors:
http://jdmfsm.info/Auto/Japan/Subaru/Impreza/
 

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Discussion Starter #8
Thanks for all your help Kennybobby, that diagram (although one wire is mislabeled) is accurate!

With the pedal at rest it reads 0.66v on the signal wire


Depress the pedal, and it climbs up to 3.2v


I guess I should have tested the resistance to try and ascertain if this uses a wiper. I will post my findings later. My crappy little power supply worked fine - it was putting out about 5.22v.
 

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Good job on ringing it out, the voltages look right in line with the FSM values.

Here is diagram for 2006 that is close but has a Red wire on pin 6, where your's is white...? subaru wiring and manuals are fubar.
 

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At half pedal, check to see if you get 1.93 or so V. If so, then the max and min you measured are the correct limit stops...for that pedal.
 
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